An embodiment of the present invention relates to the field of integrated circuits and, more particularly, to measuring relative, within-die leakage current and/or providing a temperature variation profile.
In integrated circuits, when a biased metal oxide semiconductor (MOS) transistor is turned off, a small leakage current flows through its drain to its source and substrate due to electron-hole generation, even when the gate to source voltage is zero. In deep sub-1-micron processes, gate leakage current also becomes significant, and may even augment drain leakage. These leakage currents are a source of static current in complementary metal oxide semiconductor (CMOS) very large scale integration (VLSI) integrated circuits, even when their clocks are turned off.
Among other factors, leakage currents are a function of device threshold voltage, channel length, supply voltage, and temperature. Manufacturing variations across a VLSI chip due to variations in doping, ion implantation, and lithography, for example, can cause both the threshold voltages and finished channel lengths of MOS devices to vary across the chip. Variations also occur between manufacturing wafers, lots, and revisions of any particular VLSI process. These variations can cause significant variations in leakage currents at different locations on a die.
Knowledge of leakage current variations across a die can help designers to take various actions to reduce leakage where needed, control the profile across the die and/or across process lots, perform tradeoffs between device speed and leakage, and correlate leakage current variation to manufacturing steps.
For a different aspect of VLSI chip design, testing and operation, it is desirable to obtain a relatively accurate profile of temperature variations across a die during its operation. Having such a profile may enable identification of excessive temperature rises (“hot spots”) across a die, and also may help to identify speed-limiting locations on the die during initial validation and testing, for example.